Senckenberg Forschung

b) Volcanology & Geophysics
3 Surface

b) Volcanology & Geophysics
     Geophysical potential methods are qualified for the detection of volcanite occurrences. Many known maar-diatreme
     volcanoes and other volcanic deposits are buried by post-genetic sediments. Geophysical methods resulted in their 
     initial discovery and subsequent drilling provided geological samples, which confirmed their origin. Interpretation of a
     single geophysical data set over a suspected volcanic structure can be ambiguous. When combined, however, with
     complementary geophysical methods and the existing database over other known occurrences, a more definite
     assessment can be made.
     The most notable geophysical signature associated with maar-diatreme volcanoes is a negative gravity anomaly.
     These gravity lows are generally circular and cover the whole structures. They are due to lithological and physical
     changes associated with the phreatomagmatic explosion. In well-preserved maar structures, low-density
     sedimentary infill of the maar lake contributes to the gravity low.
     In general, magnetic anomalies are more complex than gravity anomalies. Their reason is the very complex setting of
     volcanic structures and its very different magnetic properties.
     Also electrical methods are suitable for the exploration of volcanic occurrences. Due to the presence of fluids in 
     explosion-induced fractures and pore spaces the electrical resistivity levels are decreased and that can be mapped
     Reflection seismic surveys allow for detailed imaging of some volcanic structures, like maar-diatreme volcanoes.
     Geophysical well logging methods are very useful for the detailed investigation of drill holes, also in volcanic
     influenced areas.
     Contributors have been encouraged to consider these key topics.

     Peter Suhr (Freiberg/D)
     Jan Mrlina (Praha/CZ)

Key Notes  
Jan Mrlina (Prague/CZ) “Search for volcanoes based on constraining geophysics and geomorphology”